The present invention relates to a permeable image display screen incorporated into a rear projection type display apparatus.
FIGS. 19A and 19B schematically show the basic structure of a conventional rear projection type display apparatus having a permeable image display screen. FIG. 19A is a schematic perspective view of the display apparatus, and FIG. 19B is an enlarged horizontal sectional view of a section A in FIG. 19A.
In the display apparatus shown in FIGS. 19A and 19B, image light from an image generator 1 is diverging and directed toward the permeable image display screen 2. The diverging image light passes through a Fresnel lens sheet 3 and is refracted, and becomes nearly parallel light.
Thereafter, the nearly parallel light is incident on a lenticular lens sheet 4. The image light incident on the lenticular lens sheet 4 is focused by the first lens portions 4a of the lenticular lens sheet 4. The focused light is moderately diffused in horizontal and vertical directions by diffusion particles 5 and second lens portion 4b of the lenticular lens sheet 4 and then reaches the viewer's eyes. The diffusion particles 5 have a function of moderately widening an angle of view by refracting and scattering the image light. In FIGS. 19A and 19B, a reference numeral 4c denotes non-focusing portions through which the image light does not pass.
However, as shown in FIG. 19B, when the diffusion particles 5 are contained in the lenticular lens sheet 4, some diffusion particles 5 protrude from the image light emission surface of the lenticular lens sheet 4 and roughen the image light emission surface. For this reason, when the display apparatus is installed in a well-lighted place, the extraneous light is reflected at the image light emission surface and becomes scattered light, which reaches the viewer's eyes. Consequently, there arises the problem that the viewer recognizes roughness on a displayed image and can not detect the gloss and depth of the image, thereby degrading the image quality. Also, since the scattered light of the extraneous light due to the diffusion particles 5 is produced on the dark portions of the image light emission surface from which the image light does not emerge, there arises the problem that the viewer feels as if the dark portions are slightly clouded and the contrast is therefore reduced.
To overcome such problems, there is considered, for example, a countermeasure of installing a light permeable flat plate 9, as shown in FIG. 20, on the viewer's side of the lenticular lens sheet 4. However, there arises another problem that the reflected light of the extraneous light, reflected regularly at the surface of the light permeable flat plate 9, overlaps the image light, thereby considerably degrading the image quality.